Serial printer power drive and timing mechanism

ABSTRACT

Power drive and timing train mechanism for serial printer mounted in an injection molded base by means of novel plastic bearings and without the usual fastening hardware, and including jack shaft belt-driven by start-stop on demand motor and, through two electrically operated clutches, separately driving power transfer and take up reel shafts, latter lifts ribbon to active position and rotates take up reel connected to print head by novel flexible driven member and retaining coupling at each end for simplified assembly and providing superior impact and vibration dampening properties in linearly moving print head laterally and return thereof by spring. After first or take up reel clutch is deenergized to effect spring return of print head to normal position, if print head velocity exceeds predetermined value interpreted by optical switch thereon and stationary sensing rack comprising pulse generator, take up reel clutch is caused to be pulsed to reduce velocity. During return of print head to home position, paper and ribbon drives are actuated by power transfer shaft through the second clutch with that clutch being deenergized by a second optical switch.

United States Patent Wilczewski et al.

[451 Jan. 21, 1975 1 SERIAL PRINTER POWER DRIVE AND TIMING MECHANISM [75] Inventors: Robert H. Wilczewski, Roselle;

James E. Blomquist, Park Ridge, both of 111.

[73] Assignee: Victor Comptometer C0rp.,

Chicago, Ill.

[22] Filed: June 4, 1973 [21] Appl. No.: 366,473

[52] US. CL. 197/1 R, 197/68, 308/15 [51] Int. Cl. B4lj l/34 [58] Field of Search 197/16, 1 R, 68, 18, 64; 308/15, 22,238

[56] References Cited UNITED STATES PATENTS 1,056,657 3/1913 Friedman 197/68 1,451,277 4/1923 StiCkney 197/68 X 2,724,479 11/1955 Durkee 197/68 2,891,651 6/1959 Wusteney et al. 197/68 3,307,291 3/1967 Cremer 308/15 UX 3,670,861 6/1972 Zenner et al. 197/64 3,773,161 11/1973 Bossi 197/18 X Primary Examiner- Edgar S. Burr Assistant Examiner-R. T. Rader Attorney, Agent, or Firm-David, McCaleb & Lucas [5 7] ABSTRACT Power drive and timing train mechanism for serial printer mounted in an injection molded base by means of novel plastic bearings and without the usual fastening hardware, and including jack shaft belt-driven by start-stop on demand motor and, through two electrically operated clutches, separately driving power transfer and take up reel shafts, latter lifts ribbon to active position and rotates take up reel connected to print head by novel flexible driven member and retaining coupling at each end for simplified assembly and providing superior impact and vibration dampening properties in linearly moving print head laterally and return thereof by spring. After first or take up reel clutch is deenergized to effect spring return of print head to normal position, if print head velocity exceeds predetermined value interpreted by optical switch thereon and stationary sensing rack comprising pulse generator, take up reel clutch is caused to be pulsed to reduce velocity. During return of print head to home position, paper and ribbon drives are actuated by power transfer shaft through the second clutch with that clutch being deenergized by a second optical switch.

12 Claims, 7 Drawing Figures ELECTRICAL CONTROL CIRCUIT mmaw 3361510 SHEET 1!]? 3 ELECTRICAL CONTROL CIRCUIT SERIAL PRINTER POWER DRIVE AND TIMING MECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to serial printers, and more particularly to novel power drive and timing train mechanism therefor.

2. Description of the Prior Art High speed serial printers have been developed to employ a plurality of wires in a print head movable translationally and continuously relative to the impression-receiving paper as the wires are selectively moved longitudinally to effect dot impressions on the paper by means of an interposed inking ribbon to complete a line of printing, with the print head then being returned to home position, the paper fed to receive a succeeding line of printing and the ribbon fed to present another portion in active position. Such machines, however, have been very expensive, such as that of U.S. Pat. No. 3,703,949 which includes a carriage for the print head driven by a belt that is moved in a printing direction by a roller on a drive shaft rotated by a continuously energized motor through a forward clutch engaged by a solenoid, with the belt being moved in the opposite direction by the motor when that forward clutch is deenergized and a reverse clutch is engaged by a reverse solenoid to return the carriage to home position. Two additional solenoids are employed to effect paper line feed and ribbon feed.

SUMMARY OF THE INVENTION This invention provides a simplified and extremely reliable power drive and timing train for the print head of a high speed serial printer which employs only two electric clutches; the first to drive a take up reel shaft having a reel connected to the print head by a novel flexible and non-metallic drive member and retaining coupling at each end, and to lift an inking ribbon into active position; and the second, which is energized upon deenergization of the first clutch, to drive a power transfer shaft to actuate paper and ribbon feeds. Deenergization of the first or take up reel clutch causes spring return of the print head to home position. A pulse generator, including an optical switch carried by the print head and a stationary elongated strip having narrow transparent slits, causes pulsing of the take up reel clutch to reduce the print head return velocity if it exceeds a predetermined value, as interpreted by that pulse generator. The cost of making and repairing this printer mechanism is minimized by providing an injection molded base and substantially eliminating conventional fastening hardware, the take up reel and power transfer shafts being secured by novel plastic bearings snap-fitted into suitable slots in the base. The retaining couplings at the ends of the flexible drive member simplify assembly and disassembly, and the drive member has superior impact and vibration dampening properties which, with the pulsing of the take up reel clutch if the spring-driven return velocity is excessive, automatically assures accurately timed and long lived operation.

IN THE DRAWINGS FIG. 1 is a diagrammatic plan view of a serial printer power drive and timing mechanism embodying the features of this invention;

FIG. 2 is a top plan view of an injection molded base for the printer;

FIG. 3 is a front end elevation of the base as seen from the lower end of FIG. 2;

FIG. 4 is a detail vertical section, with parts broken away, as seen from the front, showing the print head, a front guide rod therefor and the transport means for reciprocably translating the print head thereon;

FIG. 5 is a detail vertical section on an enlarged scale through the connecting means on one of the ends of the flexible drive band;

FIG. 6 is a sectional view taken substantially on the line 66 of FIG. 5; and

FIG. 7 is a perspective view of one of the plastic bearings for supporting a shaft in the machine base.

DESCRIPTION OF THE PREFERRED EMBODIMENT As best seen in FIGS. I and 4, a high speed serial printer embodying this invention includes a print head, generally indicated by reference numberal 11, which in the preferred embodiment is the same as that disclosed in co-pending application for U.S. Patent Ser. No. 313,248, filed Dec. 8, 1972, and incorporates a plurality of wires each printingly operable longitudinally by a solenoid 12 like that comprising the subject matter of co-pending application for U.S. Patent Ser. No. 301,774, filed Oct. 30, 1972, and issued Jan. 22, 1974 as U.S. Pat. No. 3,787,791. The print head 11 is supported for reciprocable translation from, and return to, a home position at the right side of the machine by guide means including a stationary front rod or transversely extending horizontal shaft 13 mounted by an adjustment bracket or auxiliary frame 14 (FIG. 4) on a base indicated generally by reference numeral 15 in FIGS. 2 and 3. The front print head supporting rod 13 is the same as shaft 19 in Ser. No. 313, 248. It will be understood, of course, that this invention is applicable to other types of high speed serial printers as well as the wire printer herein illustrated.

As shown in FIG. 1, a suitable stop-start on demand motor 16 drives the driving element of a first electrically operated clutch 17, mounted on a first or take up reel shaft 18, through gearing including a gear 19 freely rotatable on shaft 18, transport gear 21 rotatably mounted on a second or power transfer shaft 22 and a jackshaft gear 23, and a timing belt 24 connected to a driving pulley on the motor shaft. Energizing clutch I7 magnetically couples gear 19 to shaft 18, the armature of the clutch being slidably mounted by a square bore on a square shoulder on the gear 19. A second similar electrically operated clutch 25 on the second or power shaft 22 when energized magnetically couples gear 21 to shaft 22 to rotate the latter, a cam 26 mounted thereon and comprising ribbon drive means, a home positioning cam 27 cooperating with a spring-urged and pivotally mounted detent lever 28 to normally retain the shaft in home position, and a worm gear 29 which is part of paper drive means (not otherwise illustrated herein) for advancing the roll of paper after completion of each line of printing by an outward translation from home position of the print head 11.

The clutches l7 and are the same as that disclosed in copending application for US. Patent Ser. No. 388,455, filed Aug. 15, 1973. The takeup reel shaft 18, power shaft 22, and ribbon drive cam 26 herein are the same as members designated, respectively, 36, 51 and 52 in'copending application for US. Patent Ser. No. 397,883, filed Sept. 17, 1973.

Each of the shafts ,18 and 22 is rotatably supported by plastic bearings, indicated generally by reference numeral 30, which are snap-fitted into the injection molded plastic base 15. The base 15 is made from a suitable reinforced phenolic thermo-set molding compound, such as that produced by Fiberite Corporation designated Fiberite 4004, and the bearings 30 are molded from acetal fiber-resin, such as that made by E. I. du Pont de Nemours and Co., Inc. under their trademark DELRIN 'AF. In order to receive and retain the bearings 30, the base 15 is formed with vertical slots or recesses 31 (FIGS. 2 and 3) terminating in and defining upper and lower horizontal surfaces 32 and 33, respectively, and having vertical grooves 34 in their side walls. Each of the plastic bearings 30 comprises a block having a main body with a shaft-receiving bore 35 (FIG. 7) and a spring finger 36 at each corner at one end spaced vertically and laterally from the body and terminating in a tip 37 with curved outer side walls normally extending beyond the body radially of the bore 35. The tips 37 of these spring finger corner portions 36 thus may be moved inwardly into or inwardly of the side surfaces of the body as the bearing is slid into a recess 32, with the several fingers being of slightly different lengths so that as the ends thereof reach the associated grooves 34, one or more of them will spring into those grooves to removably retain the bearing 30 in its proper place in the base 15 and automatically compensate for any slight dimensional differences.

As seen in FIGS. 2 and 3, the injection molded plastic base 15 also forms apertured pads 38 at its forward corners to which the adjustment bracket or auxiliary from 14 is secured, the latter supporting the front guide rod 13, a stationary elongated strip 39 having narrow transparent slits (FIG. 1) and a ribbon deck (not shown) pivotally mounted on upward and rearward extensions thereof. A transverse rail 41 (FIGS. 2 and 3) forming an integral part of the base 15 has an upwardly extending rib 42 for guiding pivotal movements of the ribbon deck. Adjacent the left end portion of the rail 41 and below it, the base 15 is provided with a forwardly extending finger 43 for anchoring an end of a print head return spring to be described hereinafter. To the rear and below the rail 41, the base is provided with an upwardly extending and horizontally apertured protuberance 44 for pivotally receiving and anchoring the lower end of a ribbon drive bellcrank (not shown) which is actuated by the same 26 of FIG. 1. To the left or protuberance 44, the base 15 is formed to provide a stud 45 for anchoring the lower end of a spring urging the ribbon deck downwardly into inactive position.

As shown in FIG. 2, the central rear portion of the base 15 is formed as a motor well having four corner bosses 46 with upper surfaces sloping downward and inward for receiving and positioning the motor 16. At its outer rear corners, the base 15 is provided with upstanding arms 47 having studs 48 extending inwardly from their upper ends for pivotally mounting a combined paper tear off blade and cams for moving platen roller trunnions (not shown) into latched engagement with upwardly extending positioning posts 49 which also are formed integrally with the base-15. It will be apparent from the foregoing that the injection molded plastic base 15 and the plastic bearings 30 substantially eliminate the need or use of conventional fastening hardware which simplifies manufacture of the parts, their assembly and any repair that might be required, and results in a less expensive and more dependable printer than those of the prior art.

Referring now to FIGS. 1 and 4-6, energization of the first electric clutch 17 causes rotation of the first shaft 18 in a counterclockwise direction as viewed from the front of the printer in FIG. 4. Secured to the shaft 18 for such rotation therewith are a ribbon deck lifting cam 51 (FIG. 1) which is the same as that designated 35 in said application Ser. No. 397,883, and a take up reel indicated generally by reference numeral 52 which is molded from a suitable plastic. The peripheral surface of reel 52 has a reentrant portion 53 continuing inward as a flat surface terminating in a curved rib 54. A substantially segmental interior wall 55 spaced radially from the inner end of curved rib 54, an inner hub portion 56 and a short angular wall 57 define an interior recess for receiving and retaining connecting means, generally designated by reference numeral 58, on the end of an elongate flexible band 59.

As best seen in FIGS. 5 and 6, the band 59 which is made from polyurethane elastomer reinforced with polyester cord, is provided on one surface with transversely extending teeth 61 adjacent each end in two groups spaced from each other by asmooth portion that is wrapped around a metal roller or eyelet 62. The two adjacent groups of teeth 61 engage each other in interlocking relationship to prevent slipping of the band 59 relative to the eyelet 62. The eyelet 62 forms a part of the connecting means 58 which also includes retaining means in the form of a molded plastic keeper 63 having a hollow main body slidable along and embracingly engaging the interlocked portions of the band 59 to prevent separation of the teeth 61 and which terminates at its outer end in curved fingers 64 for embracing the wrapped portion of the band to retain the eyelet 62 therein. It will be understood that such a connecting means 58 is provided at each end of the flexible band 59, with one disposed in the'recess in take up reel 52, as noted, and the other in a horizontally extending recess or slot 65 (FIG. 4) in the rear portion of a carriage 66 forming part of the print head 11 that is slidably supported by the front guide rod 13.

One end of a print head return coil spring 67 engages in the eyelet 62 of the connecting means 58 which is disposed in the recess 65 and its other end engages the forward extending finger 43 of the transverse rail 41 of the base 15. This coil spring 67 rides upon the periphery of a plastic roller 68 rotatably mounted by an integral stud shaft 69 supported in suitable slots formed in the outer end of the rail 41 and the rear surface of the right hand pad 38 of the base 15. Consequently, as the print head 11 is moved translationally to the left in FIGS. 1 and 4 from its home position by rotation of the take up reel 52 in response to energization of the clutch 17, the spring 67 is extended. Due to the curvature of the reentrant portion 53 of the take up reel 52, the initial increment of that translation comprises rapid acceleration of the print head to a constant velocity which is maintained by the winding of the band 59 on the cylindrical periphery of reel 52. The clutch 17 is deenergized in response to a signal given when printing of a full or partial line by print head 11 is completed, whereupon the spring 67 returns the print head 11 translationally to the right to its home position. An optical switch 71 (FIG. 1) on the print head 11 cooperates with the stationary slit strip 39 as the signal initiating portion of a pulse generating means for automatically controlling pulsing of the first clutch 17 if the returning velocity of the print head exceeds a predetermined value. This pulse generating means comprises a wellknown electrical control circuit wherein the frequency of light pulses through transparent slits in the strobe strip 39 is measured or compared with respect to a fixed frequency, the pulse generating means being operable to pulsingly energize the clutch 17 as required to provide a forward or braking action when the return velocity of the head as measured by thefrequency of light pulses exceeds a predetermined velocity represented by the fixed frequency. A known circuit suitable for this purpose is disclosed on page 673 of PULSE, DIGITAL AND SWITCHING WAVE FORMS by Millman & Taub, published in 1965 by McGraw-Hill Book Company, wherein a counter is used to measure an input frequency by comparison thereof with respect to a crystal oscillator frequency, the counter being used to control clutch energization whenever the input frequency exceeds the divided oscillator frequency by a predetermined amount. The use of such known electrical control circuit is illustrated in FIG. 1 herein by the diagrammatic representation designated 70 therein. A rearwardly extending lug 72 (FIG. 4) on the take up reel 52 contacts an upstanding flat steel leaf spring 73 (FIG. 2) having its lower end disposed in a slot in the base as the print head returns to home position, and the flexible and non-metallic band 59 provides therewith superior impact and vibration dampening during such cyclic-reciprocation of the print head. It also will be appreciated that this print head transport means reduces fabricating problems and greatly facilitates assembly, the latter being accomplished by sliding a keeper 63 onto each end of the band 59, wrapping each end of the band around an eyelet 62 and interengaging the adjacent teeth 61, and then sliding the keepers 63 outwardly to their retaining position of FIG. 5. The thus completed flexible drive means can then be installed merely by insertion of the connecting means 58 at one of its ends into the previously described recess in the take up reel 52, bringing the band 59 around the rib 54 and reentrant portion 53, and sliding the connecting means 58 at its other end into the recess 65. Subsequent hooking of one end of spring 67 into the eyelet 62 of that connecting means 58 will insure retention of the latter in the recess 65 of the print head carriage 66.

Initial counterclockwise movement of cam 51 with shaft 18 (as seen from the front of the machine) lifts the normally lowered or retracted ribbon into active position relative to the print head 11, and the cam maintains the ribbon in active position during subsequent reciprocation of the print head and permits it to drop back to lowered position as the print head returns to home position. As previously noted, the second clutch 25 is energized to rotate shaft 22 when the print head 11 has completed its active linear movement away from home position. One complete revolution thus is given to the ribbon drive cam 26 and the paper drive worm gear 29, and the clutch 25 is automatically deenergized by an electronic circuit in response to a signal sent by an optical switch 74 (FIG. 1) which cooperates with a slotted disk 75 on the shaft 22. This completes a cycle of operations of the printer, the cam 27 on shaft 22 cooperating with detent lever 28 to insure accurate stopping and retention of the shaft in home position.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. In a high speed serial printer, a unidirectional motor and a print head supported for reciprocable translation from and return to a home position; power drive and timing mechanism comprising a first shaft mounting gearing rotatable by said motor and a first clutch operable to rotate said shaft; a second shaft mounting gearing rotatable by said motor and a second clutch operable to rotate said second shaft; transport means including a takeup reel mounted on said first shaft and flexible drive means interconnecting said takeup reel and said print head for translating the latter in one direction, and spring means connected to said print head for returning the latter to said home position, said first clutch being deenergized at different times to effect return of said print head after a full or any partial line of printing has been effected and further being energized by said timing mechanism if the return velocity of said print head exceeds a predetermined value, said second clutch being energized to actuate ribbon and paper drive means while said print head is being returned to said home position; plastic bearings having longitudinally extending bores receiving said shafts exteriorly of said gearing mounted thereon; and an injection molded plastic base having slots for receiving said plastic bearings and retaining the longitudinal ends thereof in snap-fitted engagement therein to limit longitudinal movements of said shafts and said gearing mounted thereon.

2. In a printer according to claim I, wherein said spring means functions to return said print head to home position upon deenergization of said first clutch, pulse generating means for automatically effecting pulsing of said first clutch if the returning velocity of said print head exceeds a predetermined value.

3. A printer according to claim 2, wherein said pulse generating means comprises a stationary strip with narrow transparent slits mounted on said base, and an optical switch cooperating therewith and mounted on said print head.

4. A printer according to claim 1, wherein said flexible drive means comprises a polyurethane elastomer band reinforced with polyester cord to provide superior impact and vibration dampening in moving said print head.

-5. A printer according to claim 1, wherein said flexible drive means comprises an elongate band having connecting means at each end for engagement, respectively, with said print head and said take up reel, and said take up reel defines a peripheral cam surface for windingly receiving said band to accelerate said print head rapidly to a constant velocity and to maintain that velocity during outward translation of said print head from home position.

6. In a printer according to claim 1, cam means mounted on said first shaft for moving a ribbon into active position relative to said print head and maintaining said first clutch, paper and ribbon drive means actuated by the resulting rotation of said second shaft, and an optical switch cooperating with said second shaft to illi- .tiate deenergization of said second clutch after a single revolution of said second shaft.

8. A printer according to claim 1, wherein each said plastic bearing comprises a block having a main body with a said shaft-receiving bore, and spring finger corner portions at one end integral with and spaced vertically and laterally from said body with tips normally extending beyond said body radially of said bore, and said slots in said base having grooves for receiving said tips of associated said bearings to effect said snap-fitted engagement.

9. A printer according to claim 8, wherein said spring finger corner portions differ slightly from each other in length to automatically compensate for any slight dimensional variations in said base grooves and slots.

10. In a high speed serial printer having a motor and a print head supported for reciprocable translation from and return to a home position, power drive and timing mechanism comprising a first shaft mounting gearing rotatable by said motor and a first clutch operable to rotate said shaft, a second shaft mounting gearing rotatable by said motor and a second clutch operable to rotate said second shaft, transport means including a takeup reel mounted on said first shaft and flexible drive means interconnecting said takeup reel and said print head for reciprocably translating the latter, plastic bearings on said shafts, and an injection molded plastic base having slots for receiving said plastic bearings and retaining the same in snap-fitted engagement therein, wherein said flexible drive means comprises an elongate band having connecting means at each end'for engagement, respectively, with said print head and said takeup reel, and said takeup reel defines a peripheral cam surface for windingly receiving said band to accelerate said print head rapidly to a constant velocity and to maintain that velocity during outward translation of saidprint head from position, and wherein each said connecting means comprises an eyelet around which an end of said band is wrapped and retaining means slidable along said band and embracing the wrapped portion thereof to retain said eyelet therein 11. A printer according to claim 10, wherein one surface of said band is providedwith transversely extending' teeth adjacent each end interlocking when said band is wrapped around said eyelets to prevent slipping thereof relative to said eyelets.

12. A printer according to claim 11, wherein said retaining means embracingly engage said band to prevent separation of said interlocking teeth. 

1. In a high speed serial printer, a unidirectional motor and a print head supported for reciprocable translation from and return to a home position; power drive and timing mechanism comprising a first shaft mounting gearing rotatable by said motor and a first clutch operable to rotate said shaft; a second shaft mounting gearing rotatable by said motor and a second clutch operable to rotate said second shaft; transport means including a takeup reel mounted on said first shaft and flexible drive means interconnecting said takeup reel and said print head for translating the latter in one direction, and spring means connected to said print head for returning the latter to said home position, said first clutch being deenergized at different times to effect return of said print head after a full or any partial line of printing has been effected and further being energized by said timing mechanism if the return velocity of said print head exceeds a predetermined value, said second clutch being energized to actuate ribbon and paper drive means while said print head is being returned to said home position; plastic bearings having longitudinally extending bores receiving said shafts exteriorly of said gearing mounted thereon; and an injection molded plastic base having slots for receiving said plastic bearings and retaining the longitudinal ends thereof in snap-fitted engagement therein to limit longitudinal movements of said shafts and said gearing mounted thereon.
 2. In a printer according to claim 1, wherein said spring means functions to return said print head to home position upon deenergization of said first clutch, pulse generating means for automatically effecting pulsing of said first clutch if the returning velocity of said print head exceeds a predetermined value.
 3. A printer according to claim 2, wherein said pulse generating means comprises a stationary strip with narrow transparent slits mounted on said base, and an optical switch cooperating therewith and mounted on said print head.
 4. A printer according to claim 1, wherein said flexible drive means comprises a polyurethane elastomer band reinforced with polyester cord to provide superior impact and vibration dampening in moving said print head.
 5. A printer according to claim 1, wherein said flexible drive means comprises an elongate band having connecting means at each end for engagement, respectively, with said print head and said take up reel, and said take up reel defines a peripheral cam surface for windingly receiving said band to accelerate said print head rapidly to a constant velocity and to maintain that velocity during outward translation of said print head from home position.
 6. In a printer according to claim 1, cam means mounted on said first shaft for moving a ribbon into active position relative to said print head and maintaining the same therein during translation of said print head.
 7. In a printer according to claim 1, wherein said second clutch is energized in response to deenergization of said first clutch, paper and ribbon drive means actuated by the resulting rotation of said second shaft, and an optical switch cooperating with said second shaft to initiate deenergization of said second clutch after a single revolution of said second shaft.
 8. A printer according to claim 1, wherein each said plastic bearing comprises a block having a main body with a said shaft-receiving bore, and spring finger corner portions at one end integral with and spaced vertically and laterally from said body with tips normally extending beyond said body radially of said bore, and said slots in said base having grooves for receiving said tips of associated said bearings to effect said snap-fitted engagement.
 9. A printer according to claim 8, wherein said spring finger corner portions differ slightly from each other in length to automatically compensate for any slight dimensional variations in said base grooves and slots.
 10. In a high speed serial printer having a motor and a print head supported for reciprocable translation from and return to a home position, power drive and timing mechanism comprising a first shaft mounting gearing rotatable by said motor and a first clutch operable to rotate said shaft, a secoNd shaft mounting gearing rotatable by said motor and a second clutch operable to rotate said second shaft, transport means including a takeup reel mounted on said first shaft and flexible drive means interconnecting said takeup reel and said print head for reciprocably translating the latter, plastic bearings on said shafts, and an injection molded plastic base having slots for receiving said plastic bearings and retaining the same in snap-fitted engagement therein, wherein said flexible drive means comprises an elongate band having connecting means at each end for engagement, respectively, with said print head and said takeup reel, and said takeup reel defines a peripheral cam surface for windingly receiving said band to accelerate said print head rapidly to a constant velocity and to maintain that velocity during outward translation of said print head from position, and wherein each said connecting means comprises an eyelet around which an end of said band is wrapped and retaining means slidable along said band and embracing the wrapped portion thereof to retain said eyelet therein.
 11. A printer according to claim 10, wherein one surface of said band is provided with transversely extending teeth adjacent each end interlocking when said band is wrapped around said eyelets to prevent slipping thereof relative to said eyelets.
 12. A printer according to claim 11, wherein said retaining means embracingly engage said band to prevent separation of said interlocking teeth. 